On the chromatic number of two generalized Kneser graphs

Abstract

We determine the chromatic number of some graphs of flags in buildings of type $A_4$, namely of the Kneser graphs of flags of type $\{2,4\}$ in the vector spaces $GF(q{)}^5$ for $q\ge 3$, and of the Kneser graph of flags of type $\{2,3\}$ in the vector spaces $GF(q{)}^5$ for large $q$.

20 pages